The review, led by Sir Michael Cullen, was commissioned by Bay of Plenty Regional Council.

It was initially due to be completed by July but the review panel was given extra time due to the amount and complexity of the information.

A farmer drives through flood waters on Otaiki Road the morning after the town of Edgecumbe was flooded by a burst stopbank. Photo: RNZ/ Brad White

Delivering the findings in Whakatāne this afternoon, Sir Michael said the College Road floodbank failed because water found its way through the material underneath the wall.

He said the seepage may have been increased by flaws in the foundation fill of the wall and damage from the town's 1987 earthquake and 2004 flood.

Sir Michael told Checkpoint with John Campbell the review also found that many Edgecumbe residents were insufficiently aware of the risks of serious flooding and there were no plans for precautionary evacuation.

"It needs to be trigger points, which are much more realistic for evacuating people from those urban areas, and there's many hours available because you're getting reasonably decent information, which tells you that there are likely to be serious problems."

The Bay of Plenty Regional Council has said there were lessons to be learnt from the Edgecumbe flood, including having a better idea of risk and a more conservative evacuation plan.

Council chairman Doug Leeder said they were taking the findings on board.

"Going forward we have to approach the management of risk and the potential for evacuation in a lot more conservative manner.

"The event in 2004 and the event in 2017 have clearly highlighted to Regional Council and to the community that the underlying geology on which these flood banks have been built is inadequate to serve the purpose for what they are now."